1. Field of the Invention
The present invention relates generally to scroll compressors which include fixed and orbiting scroll members and, more particularly, to a valve which regulates a pressure intermediate suction and discharge pressures to maintain sealing axial engagement between the orbiting scroll member and the fixed scroll member.
2. Description of the Related Art
A typical scroll compressor comprises two facing scroll members, each having an involute wrap wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other member, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port. The pockets thereby convey and compress a fluid, typically a refrigerant, contained therein.
During compressor operation, the pressure of the compressed refrigerant tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face of the other scroll member. Such leakage reduces the operating efficiency of the compressor and, in extreme cases, may result in the inability of the compressor to operate.
Efforts to counteract the separating force applied to the scroll members during compressor operation, and thereby minimize the aforementioned leakage, have resulted in the development of a variety of axial compliance mechanisms. For example, it is known to axially preload the scroll members toward each other with a force sufficient to resist the dynamic separating force. One approach is to assure close manufacturing tolerances for the component parts and have a thrust bearing interface between the fixed and orbiting scroll members for conveying axial forces between the members. The most common approach is to feed back compressed refrigerant gas to urge the two scroll members together.
Typically, the axial compliance forces bias the tips of the scroll compressor wraps against the inner surface of the opposite scroll and/or may bias sliding surfaces on the outer perimeter of the two scroll members into mutual engagement. Frictional forces are created at these areas of contact as the moveable scroll is orbited about the fixed scroll. Excessive frictional forces generated by the axial compliance mechanism can increase the power required to operate the scroll compressor and have an abrasive effect on the engagement surfaces. The abrasive effects created by the axial compliance forces can damage or lead to excessive wearing of the wrap tips and interior surfaces, or faces, of the two scrolls when the axial compliance forces are borne by these surfaces and thereby negatively impact the sealing ability and longevity of the wrap tips.
Some prior art scroll compressors provide passageways in the orbiting scroll member plate through which a portion of the compression chamber formed by the interfitting scroll wraps, in which refrigerant is at intermediate pressure, is in direct fluid communication with an intermediate pressure chamber formed in part by the side of orbiting scroll member opposite that on which scroll wraps are disposed. The refrigerant gas in the intermediate pressure chamber exerts an axial sealing force between the orbiting and fixed scroll members. However, under certain operating conditions, such as on compressor startup, such arrangements can create intermediate pressures greater than discharge pressure, forcing the fixed and orbiting scroll members together too tightly, resulting in compressor inefficiency. Conversely, where suction pressures are very low intermediate pressures may also be low, and such arrangements can provide inadequate axial sealing force between the fixed and orbiting scroll members. A method of regulating the intermediate pressure to bias the fixed and orbiting scroll members into consistent and proper sealing engagement under varying compressor operating conditions is needed.